B1=1/3 q=1/3 Bn=1/6561 n-? Sn-?

т.к |q|<1, то Sn=b1/1-qbn=b1*q^n1/6561=(1/3)*(1/3)^n1/3^8=1/3^(n+1)3^8=3^(n+1)n+1=8; n=7Sn=(1/3)/(2/3)=1/2=0,5Ответ: n=7; Sn=0,5